1. Field of the Invention
This invention relates to detection systems using ultra-wideband (UWB) pulses to detect magnetic resonance responses, to receivers for such systems, and to corresponding methods and software for carrying out the methods, and to methods of using UWB pulses to activate tags having a magnetic resonance response and to tags for such apparatus and methods.
2. Description of the Related Technology
Radar is well known and is based on the property that metallic objects cause strong reflection of electromagnetic radiation in air due to strong impedance contrast. Metallic objects have a complex wave impedance, approximately equal to Z=(1+j)/σδ with δ the characteristic depth of penetration of the waves, also called the skin depth. The waves will penetrate at the metal surface over a couple of skin depths and some absorption may occur in that surface layer. Most of the power will reflect at the metal surface. U.S. Pat. No. 5,766,208 mentions that if a metallic object such as a pace maker is present in the body, then the reflected signal will be dominated by the pace maker reflection, since the reflection coefficient approaches 1.0 for the metal object. US2005/0096589 mentions the use of an ultra-wideband or impulse radar (UWB) in order to probe the position of a catheter with magnetic tip, from which the backscattered electromagnetic radiation is measured while guiding its position using magnetic gradient forces. Only the reflection, caused by the contrast between the dielectric properties of the normal tissue and the catheter tip is used to detect the tip in this case (similar to metallic tags). Moreover, the magnetic fields used for the guidance of the catheter change the magnetic resonance continuously, thereby complicating the use of the resonant feature as a unique signature.
The use of magnetic medium to act as identification tags is already applied in magnetic RF-ID tags that consist of a magnetic medium which is detected when the article to which it is attached passes through a detection system, which emits an alternating narrow-band magnetic interrogation field of 50 Hz-100 KHz. Several patents (e.g. U.S. Pat. No. 4,940,966) discuss inventive magnetic bar coding or tagging principles based on distinctive physical parameters (e.g. shape, magnetic material, distance and orientation with respect to another tag). UWB radar technology is known for positioning of large articles (e.g. car identification, through wall vision) and motion sensing. An overview on the patents created on UWB is available at: http://www.aetherwire.com/CDROM/General/Numbers.html Some of the most relevant patents here are: Time-of-Flight Radio Location System [U.S. Pat. No. 5,661,490 and U.S. Pat. No. 5,510,800], Time Domain Radio Transmission-System [U.S. Pat. No. 4,979,186] and UWB radar motion sensor [U.S. Pat. No. 5,361,070]
Also known are pulsed magnetrons at GHz frequencies, used for heating molecules (i.e. food). These are narrow-band and no tags are involved.
Use of UWB technology is known in medicine as follows:                radar technology, [e.g. fetal heart and breath rate and uterine contractions as shown in http://www.uniroma2.it/fismed/UWBradar/MedicalUWB.html, U.S. Pat. No. 5,766,208 and WO2004107954]        UWB signal communications to send/receive (implanted) biosensor readings as time domain pulse trains E.g. US2004100376. Such a biosensor can indicate biochemical (infections, hormones) but also physical (e.g. monitoring uterine contractions using electrodes on the body etc.) events.        
Also known is Magnetoradar: Detection of mechanically excited object at a harmonic frequency of a varying magnetic field utilizing UWB radar motion sensors, as shown in U.S. Pat. No. 6,914,552.
Ferro- and ferri-magnetic nanoparticles are known for use as contrast agent in MR (Magnetic Resonance) imaging applications (at low frequencies) and for FMR imaging [U.S. Pat. No. 6,924,150].
UWB is known for scanning and imaging applications [WO03042919].
Magnetic RF-ID tags are known in U.S. Pat. No. 4,940,966 and implantable resonator circuits (LC tanks) including magnetic material in the inductor are shown in US2004138554 and US2005179552.
Magnetothermia (heating/destroying of cells) by specific uptake of nanoparticles and selective heating using AC magnetic fields below approx. 1 MHz is known. Heating of substrates by electromagnetic radiation at ferromagnetic resonance frequencies (1-300 GHz) is shown in US2004026028 and in [John Moreland, et al., Rev. of Sci. Instr., Vol 71 p 3088].
Current UWB systems have limited spatial accuracy in free space, in the human body with high refraction indices at UWB frequencies, sub mm position accuracy is possible if the signal losses are not too high. Current UWB systems have low signal-to-noise and signal-to-clutter ratio (for given maximal value of the Specific Absorption Rate (SAR-value) given by official regulations) due to high losses at high frequency in the body and multipath reflections.